This invention relates to chains, and, more particularly to pintle type conveyor chains made of a polymeric material.
Several problems have been encountered in the polymeric chains of the prior art. For example, it has been difficult to find a pin which will be retained in the link when there are forces present which tend to flex the sidebars relative to each other. There is a tendency in the chains of the prior art for the pins to work their way out of the link if the sidebars move relative to each other. Knurls have been used on one end of a chain pin in an attempt to retain the pin in the link. However, if the knurled end of the pin ever begins to turn relative to the sidebar, the knurls in the pin tend to cut into the aperture in the sidebar until the pin becomes loose.
Pins with a D-shaped cross-section have been used, but they present a problem because they reduce the cross-section of the pin throughout its length and because either the sidebars of one link or the barrel of the next adjacent link will be bearing against the flat surface portion of the pin rather than on the semicylindrical surface, thereby resulting in stress concentration at the corners of the sidebar holes, which weakens the link, or resulting in contact between the barrel and the flat surface portion of the pin, which reduces wear life.
Some of the pins of the prior art are formed by pressing a cylindrical piece of metal between dies to form it into the desired shape. This becomes more difficult as the pin becomes larger in diameter and more material has to be moved in the forming process.
Another problem encountered in pintle type links which are molded of a polymeric material is that flexing of the sidebars relative to each other tends to cause fatigue cracking in the link.